<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      padding: 0;
      margin: 0;
    }
    i {
      font-style: normal;
    }
    a {
      user-select: none;
      cursor: pointer;
    }
    a.active {
      color: red;
    }
    .footnav {
      display: flex;
      position: absolute;
      width: 100%;
      min-width: 320px;
      bottom: 0;
      height: 50px;
      justify-content: space-around;
      align-items: center;
      background-color: #F0F0F0;
    }
    .footnav a {
      display: flex;
      flex-direction: column;
      justify-content: center;
      align-items: center;
      flex-grow: 1;
    }
  </style>
</head>
<body>
  <div class="footnav">
    <a class="active">
      <i>☏</i>
      <span>视频</span>
    </a>
    <a>
      <i>☣</i>
      <span>题库</span>
    </a>
    <a>
      <i>✉</i>
      <span>留言</span>
    </a>
    <a>
      <i>☠</i>
      <span>我的</span>
    </a>
  </div>
  <script>
    document.querySelectorAll('.footnav a').forEach(function(item1,i){
      item1.onclick = function(){
        document.querySelectorAll('.footnav a').forEach(function(item2){
          item2.classList.remove('active');
        });
        this.classList.add('active');

      }
    })
  </script>
</body>
</html>